1. Field of the Art
This invention relates to power transmission chains and, more particularly, to chains and chain belts used with continuously variable transmissions or variable-pulley transmissions.
2. Discussion of the Related Art
Chains or chain belts are conventionally utilized in power transmission applications, such as the transmission of power in automotive transmissions, engine timing applications, or industrial power transmission applications. Such chain belts are also utilized in vehicle transmissions of the type known as variable-pulley or continuously variable transmissions (CVTs). A CVT typically includes a pair of pulleys of variable or adjustable effective diameter that are placed on a pair of spaced shafts. An endless chain or loop connects the pulleys to transmit power between the shafts.
One type of an endless chain belt placed across variable diameter pulleys for power transmission is one which has a first chain and a second chain, or a pair of chain portions, with a plurality of interleaved, long-plate shaped link plates connected by pins. The two chains are interconnected in a parallel, but longitudinally offset or phased relationship. Parallel load block members, also known as struts or belt blocks, are placed at a predetermined interval or spacing along the length of the first and second chains for the transmission of load or power, such that each belt block extends in the direction parallel to the direction of width of the first and second chains. The belt blocks are pinch-pressed between the opposed surfaces of the V-shaped groove of each variable pulley and are associated alternately with the first and second chains. An example of such a phased power transmission chain belt for a CVT is described in Publication JP-A-2-118230 (published in 1990) of unexamined Japanese Patent Application.
An example of a belt block or load block member of the prior art is indicated at 200 in FIG. 13. The load block 200 used in the above-described conventional chain belt includes a first part 202 and a second part 204, which are located on opposite sides of transverse centerline C. A rectangular through-hole 206 is formed in the first part 202 in a rectangular frame form. The second part 204 has a cut-out 208 at its upper portion, and a bottom portion which consists of an extension from the bottom portion of the rectangular frame of the first part 202.
Either the first chain or second chain is inserted through the through-hole 206 of the first part 202 such that this chain is not movable relative to the load block, and the other of the first and second chains is received by the cut-out 208 of the second part 204. A certain predetermined distance .DELTA.h is provided between inner wall surface 210 of the through-hole 206 and top surface 212 of the second part 204 in the radial direction of the variable V-pulley, which is the vertical direction as seen in FIG. 13. The distance .DELTA.h is provided so that contact is prevented between the second part 204 and the inner peripheral surface or inner-side end face of the link plates that are received in the cut-out 208. Such contact would occur due to a relative up and down motion or radial motion of the first chain and second chain when the link plates come into engagement with the V-groove of the V-pulley or leave the V-groove.
However, in the load block 200 of the conventional chain belt, the rigidity of the rectangular frame of the first part 202 is much greater than the rigidity of the second part 204. Accordingly, stress is concentrated at the boundary between the first part 202 and second part 204 during power transmission between the V-pulleys, which limits the endurance strength of the load block 200 in some applications of the chain belt. Also, on account of the provision of the distance .DELTA.h, which prevents the contact of the link plates and the load block due to the relative radial motion of the first and second chains, the shape of the belt block 200 is complex and its manufacture is difficult.